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超低碳贝氏体钢快速加热奥氏体长大过程中移动晶界上硼的反常偏聚 总被引:4,自引:1,他引:3
利用径迹显微照相技术研究了超低碳贝氏体钢焊接热影响区在焊接热循环快速加热过程中硼在奥氏体晶界上的偏聚行为。发现以高密度位贝氏体为原始组织的材料进行快速加热时,新形成的奥氏体晶粒边界上在很高温度下仍会出现反常的晶界硼偏聚。用晶界位错驰原制对这种新的非平衡现象进行了讨论。 相似文献
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《钢铁研究学报》2018,(11)
用场发射扫描电子显微(FE-SEM)和透射电镜(TEM)结合能谱仪,观察热轧中锰TRIP钢在不同退火温度、相同时效制度下的P偏聚行为。结果显示,650℃退火+时效后的试样更容易观察到P偏聚区,呈散点状,较为弥散地分布在视场内,而750℃退火+时效后的试样P偏聚更为集中,呈狭长带状分布,偏聚区集中而数量少。2种退火温度下,试样中的P偏聚区都与碳化物重叠分布在一起。650和750℃均为试样临界区(铁素体+奥氏体)温度,同一温度下,P在铁素体中的扩散系数是在奥氏体中的扩散系数的26倍,P更容易在铁素体晶界偏聚,但扩散系数不足以解释退火温度对于P偏析的影响。根据电子背散射衍射(EBSD)菊池线分析,含P析出相主要为正交系的FeP相及Mn_xFe_(1-x)P的(Fe、Mn)P固溶相,与Fe-Mn-C-P系优势区图计算结果一致,属于FeP相与Mn_7C_3碳化物相共存区。 相似文献
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介绍了用溶质非平衡偏聚理论研究INCONEL 718合金中硼的晶界偏聚所取得的最新进展.这些进展包括用非平衡晶界偏聚动力学理论预报热处理工艺对合金晶界脆性的影响. 相似文献
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钢中界面的化学成分、晶体结构、电子结构及其在变形、加热等外部环境作用下的演变行为等都深刻影响着钢的力学和化学行为,主导控制钢的力学、化学和加工性能。钢中界面往往是钢中新相的核点、变形的结点、裂纹的起点、腐蚀的源点。在一定程度上讲,弄清钢中界面科学问题,也就知道了钢失效的本质和提高钢质量的方向。在钢中界面科学研究(Ⅰ)的基础上,以钢中界面为研究对象,详细综述了界面对钢相变行为和服役使用性能的影响。分析了相界及相界成分或析出物偏聚对奥氏体向铁素体转变、奥氏体向贝氏体转变和逆转奥氏体相变的影响;探讨了界面以及界面成分偏聚对强度、塑性和韧性的影响;阐述了孪晶界、相界以及夹杂物/基体之间的界面在疲劳裂纹萌生和扩展方面起到的作用;重点关注了晶界、孪晶界调控以及晶界偏聚调控提高耐腐蚀性能的机理以及应用;分析了各种界面类型对抗氢脆性能的影响并简述了界面在蠕变性能劣化中起到的作用。同时简单介绍了机器学习在界面研究方面的应用,并指出了钢在服役性能中面临的界面科学问题以及今后重点研究方向的建议。 相似文献
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使用电子背散射衍射技术研究了低C高Mn高Nb成分设计下,非再结晶奥氏体变形及加速冷却速率对低碳贝氏体组织取向差特征和大角晶界分布的影响.结果表明,与原奥氏体晶粒内部的相变组织相比,原奥氏体晶界附近具有更高的大角晶界密度,非再结晶区奥氏体变形及快速冷却都有利于提高共格相变的驱动力、弱化变体选择以及有效增加大角晶界密度.此外,非再结晶区的大变形除了可充分压扁奥氏体晶粒和增加单位面积的奥氏体晶界密度外,还导致奥氏体晶界上细小的非共格转变铁素体晶粒生成,且这些铁素体晶粒与相邻组织表现出大取向差. 相似文献
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Grain boundary segregation during temper embrittlement of an Sb-containing, Ni-Cr steel has been examined both by Auger electron analysis and by chemical analysis by neutron activation of residues of surface layers dissolved by etching intercrystalline fracture surfaces. No grain boundary segregation of either alloying additions or impurities was detected during austenitization or tempering. Redistribution of Cr, Ni, and Sb between carbide and ferrite was observed during tempering, but no grain boundary segregation was noted. Both Ni and Sb were observed to segregate to the boundaries during embrittling. The segregated Sb was shown to be uniformly distributed along the prior austenitic grain boundaries and to control the ductile brittle transition temperature of the alloy studied. Ni segregating to the prior austenitic boundaries during embrittling was shown to be localized in a phase other than the ferritic portions of the boundaries. A possible location was shown to be the ferritecarbide interfaces in the grain boundaries. Weakening of these normally tenacious carbide and ferrite interfaces could account for the change in mode of brittle failure from transcrystalline cleavage to intercrystalline along the prior austenitic grain boundaries that is observed in temper brittle steels. 相似文献
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Equilibrium grain-boundary segregation and the effect of boron in B-doped Fe−3wt%Ni austenitic alloy
《Acta Metallurgica Materialia》1991,39(5):909-914
The equilibrium segregation of boron at grain boundaries and the relation between grain boundary hardening and segregation in B-doped Fe−30 wt%Ni austenitic alloy were studied with the methods of microhardness measurement and Particle Tracking Autoradiography (PTA). It was found that equilibrium segregation of boron at grain boundaries appeared in the alloy as annealed between 650 and 960°C and no segregation of boron appeared above 1050°C. It could be concluded that an excess grain boundary hardening by addition of boron to the alloy was caused by the grain boundary segregation of boron. 相似文献
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Joon Jeong Yi In Sup Kim Hyung Sup Choi 《Metallurgical and Materials Transactions A》1985,16(7):1237-1245
Partial austenitization during the intercritical annealing of an Fe-2.2 pct Si-1.8 pct Mn-0.04 pct C steel has been investigated on four kinds of starting microstructures. It has been found that austenite formation during the annealing can be interpreted in terms of a carbon diffusion-limited growth process. The preferential growth of austenite along the ferrite grain boundaries was explained by the rapid carbon supply from the dissolving carbide particles to the growing fronts of austenite particles along the newly formed austenite grain boundaries on the prior ferrite grain boundaries. The preferential austenitization along the grain boundaries proceeded rapidly, but the austenite growth became slowed down after the ferrite grain boundaries were site-saturated with austenite particles. When the ferrite grain boundaries were site-saturated with austenite particles in a coarse-grained structure, the austenite particles grew by the mode of Widmanstätten side plate rather than by the normal growth mode of planar interface displacement. 相似文献
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Optimizing the boron effect 总被引:1,自引:0,他引:1
G. F. Melloy P. R. Summon P. P. Podgursky 《Metallurgical and Materials Transactions B》1973,4(10):2279-2289
The effects of boron content varying from 0.0001 to 0.0110 wt pct were studied to determine the optimum boron range for commercially
desirable combinations of hardenability and notch toughness in 11/4 in. thick steel plate made from grade ASTM A514-J. Increasing
boron content up to 0.0025 pct resulted in a gradually increasing boron hardenability factor which reached a maximum value
slightly greater than 3 at about 0.0020 boron content. The increase in the boron hardenability factor was accompanied by a
modest decrease in the CV15 TT. An optimum value was realized at about 0.0020 pct boron. This behavior is consistent with established theory that small
amounts of boron, not detectable by conventional means, concentrate at the prior austenite grain boundaries suppressing the
ferrite reaction and thus improving hardenability. Increasing the boron content above 0.0025 pct resulted in a decrease in
the boron hardenability factor to a value of about 2.0 when 0.0060 boron was added. No further lowering of the boron hardenability
factor was experienced with boron additions as high as 0.0110 pct. Additions of boron above 0.0025 pct caused a strong increase
in the CV15 TT value. The deterioration of both the boron hardenability factor and toughness, when boron contents exceeded 0.0025 pct,
was attributable to the formatipn of large particles of the “boron constituent,” identified as Fe23(C, B)6 which formed at the prior austenite grain boundaries and nucleated massive ferrite. The mechanism was operable at austenitizing
temperatures and cooling rates equivalent to those used in commercial practice.
This paper is based on a presentation made at a symposium on “Hardenability” held at the Cleveland Meeting of The Metallurgical
Society of AIME, October 17, 1972, under the sponsorship of the IMD Heat Treatment Committee. 相似文献
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Bernadette Weisgerber Michael Hecht Klaus Harste Herv Morand Matthieu Kandel Jean‐Yves Lamant 《国际钢铁研究》2002,73(1):15-19
Peritectic steel grades are very sensitive to microcracking along austenitic grain boundaries in continuous casting. Irsid and Aktiengesellschaft der Dillinger Hüttenwerke (DH) have combined laboratory studies and industrial trials to improve surface quality on these sensitive grades. Laboratory studies at Irsid confirmed the hypothesis that a very thin layer of ferrite along austenitic grain boundaries is detrimental for cracking and indicate that the risk of cracking decreases as soon as ferrite ratio is above 10 %. Dilatometric investigations demonstrate that there is a strong shift between thermodynamic equilibrium and beginning of γ→α phase transformation under casting conditions. Furthermore, at the slab surface, there is no cyclic transformation γ→α→γ induced by thermal cycling in front of spray nozzles and supporting rolls. DH performed trials with various cooling strategies on its new vertical caster No. 5. No cracks appear with intensive cooling whereas microcracks are present with soft cooling. These results are in agreement with laboratory studies. Intensive cooling is the standard condition at DH. With this process, microcracking is avoided for all slab formats. 相似文献
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《Acta Metallurgica》1988,36(1):13-24
A combination of TEM, FIM, AP and IAP has been used to study boron grain boundary segregation in austenitic stainless steels of the types 316L (with 40 ppm or with <1 ppm boron) and “Mo-free 316L” (23 ppm boron). High resolution segregation profiles were determined for cooling rates from 0.29 to 530°C/s for three starting temperatures: 800, 1075 and 1250°C. Boron grain boundary segregation was found after all heat treatments. The segregation behaviour was mainly of the nonequilibrium type after cooling from 1075 or 1250°C whereas equilibrium segregation dominated after rapid cooling from 800°C. The influence of the relative grain orientation on the amount of non-equilibrium segregation was small for general boundaries. However, no segregation was detected at coherent twin boundaries. The binding energy of boron to austenite grain boundaries was estimated at 0.65 ± 0.04 eV for both types of steels. The influence of the composition and boron content of the steels on the segregation behaviour is discussed and the experimental techniques used are presented. 相似文献
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S. S. Babu S. A. David J. M. Vitek M. K. Miller 《Metallurgical and Materials Transactions A》1996,27(3):763-774
Improvement in high-temperature creep-rupture properties of type 308 stainless steel welds due to the controlled addition
of boron is related to microstructural evolution during welding and thermal phase stability at creep service temperatures.
The microstructure of boron-containing type 308 austenitic stainless steel welds, in the as-welded state, consisted of 8 to
10 pct ferrite in an austenite matrix. Atom probe field ion microscopy studies revealed segregation of boron and carbon to
ferriteaustenite boundaries in the as-welded state; the segregation level was less than one monolayer coverage. On aging at
923 K for 100 hours, M23C6 carbides precipitated at ferrite-austenite boundaries. On further aging at 923 K for 1000 hours, the ferrite transformed
into σ phase. Similar microstructural evolution was observed in a type 308 stainless steel weld without boron addition. The
volume fractions of M23C6 carbides were identical in boron-containing and boron-free welds. Atom probe results from the welds with boron addition in
the aged condition showed that the boron dissolved in the M23C6 carbides. However, lattice parameter analysis showed no apparent difference in the extracted carbides from the welds with
and without boron. Creep property improvement due to boron addition could not be related to any change in the volume fraction
of carbides. However, the results suggest that the incorporation of boron into M23C6 carbides may reduce the tendency for cavity formation along the M23C6 carbide-austenite boundaries and hence improve the resistance to creep fracture. The observed microstructural evolution in
welds is consistent with thermodynamic calculations by THERMOCALC software. 相似文献
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《Acta Metallurgica》1987,35(7):1767-1774
The twinning frequency expressed as the number of coherent twin boundaries per grain has been investigated as a function of grain size in type 316 and 316L commercial austenitic stainless steels with different carbon contents as well as doped with 30ppm of boron, and subjected to various thermomechanical treatments. Experiments have established that the number of coherent twin boundaries per grain (TB/grain) for grain sizes larger than 0.1 mm, increases linearly with grain size according to the equation: TB/grain = A + Ktd, where A and Kt are constants and d is the true volume grain diameter. In the ultrafine and fine grain size range from 1.5 to 100 μm the number of twins per grain is the lowest one and virtually independent of grain size. Both the increase in carbon content by 0.01% and doping with 30 ppm of boron, significantly suppress the formation of twins. Also, the rate of twins formation depends on whether twins are formed during pure grain growth or simultaneous recrystallization and grain growth. The results obtained are explained in terms of the classical Fullman-Fisher theory of twins formation. 相似文献
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Hyun Uk Hong In Soo Kim Baig Gyu Choi Young Soo Yoo Chang Yong Jo 《Metallurgical and Materials Transactions A》2012,43(1):173-181
The effects of grain boundary serration on boron segregation and liquation cracking behavior in a simulated weld heat-affected
zone (HAZ) of a wrought nickel-based superalloy 263 have been investigated. The serrated grain boundaries formed by the developed
heat treatment were highly resistant to boron segregation; the serrated sample contained 41.6 pct grain boundaries resistant
to boron enrichment as compared with 14.6 pct in the unserrated sample. During weld thermal cycle simulation, liquated grain
boundaries enriched with boron were observed at the peak temperature higher than 1333 K (1060 °C) in both unserrated and serrated
samples; however, serrated grain boundaries exhibited a higher resistance to liquation. The primary cause of liquation in
this alloy was associated with the segregation of the melting point depressing element boron at grain boundaries. The hot
ductility testing result indicated that the serrated grain boundaries showed a lower susceptibility to liquation cracking;
the grain boundary serration led to an approximate 15 K decrease in the brittle temperature range. These results reflect closely
a significant decrease in interfacial energy as well as a grain boundary configuration change by the serration. 相似文献
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分析了在控轧、控轧加回火、调质等不同工艺条件下,硼对低焊接裂纹敏感性钢显微组织和力学性能的影响。结果表明,硼抑制先共析铁素体形成,提高淬透性,在控轧工艺下含硼钢形成粗大的贝氏体和马氏体组织,并保留了原始奥氏体晶界;调质工艺得到回火索氏体组织,但含硼钢的大角度晶界比例与无硼钢相比较低。硼在强度上的作用显著,上述3种工艺下含硼钢的抗拉强度分别比无硼钢高300, 214, 101MPa,屈服强度分别高320,259,144MPa,但伸长率和冲击韧性均有所降低。无硼钢在调质工艺下、含硼钢在控轧加回火工艺下具有较好的强韧性匹配。 相似文献